Various methods for the compression of video signals are known, employing various compression standards. The example will be taken here of the MPEG2 standard.
A common criticism of the MPEG2 standard is that it has only been specified to handle video signals at 8-bit resolution. However, more and more applications are demanding the use of video signals of higher bit resolution, particularly large screen applications where the “contouring” of 8-bit signals is especially visible.
Several systems have already been proposed that allow video signals having a larger resolution or data range to be passed through the 8-bit MPEG compression system. One such scheme proposes passing the 8 most significant bits of a higher bit depth video signal through a standard 8-bit MPEG encoder and passing two least significant bits through an additional uncompressed private data channel, multiplexed with the MPEG video and audio signals for transmission. The two LSBs are then re-combined with the 8-bit compressed video signal by a special decoder. However, this scheme does not function without the extra private data channel, which adds complexity.
An alternative approach has applied some non-linear “companding” to the input video that squeezes a 10-bit input signal in to an 8-bit data range, with greater precision being applied over the brightness ranges where contouring is most visible. However, such an approach is also incompatible with standard 8-bit components, in particular standard decoders, which do not support the inverse companding feature.